OMG, how did I miss this thread until now?! I love designing creatures!

I know by now it's too late for ideas to be used for DA:2, but I'm sure the franchise has a long life ahead of it.
What about Magically or Alchemically altered chimeras? Creatures of mundane origin transformed into more deadly and twisted versions. Not like the half this, half that chimeras of Full Metal Alchemist, mind you. But rather, say you took an anfibeous newt like creature, and transformed it into a nearly man-sized monster used to protect some Mage's stronghold in a desolate swamp. I imagine Mages in most parts of the world would have to go to great length and inhabit some of the most feared and uninhabitable wilds to protect themselves from the Chantry. It could make for a very compelling story with interesting new enemy tactics in a future game.
Also, a type of possessed corps I remember reading about... I think it's Eastern European lore. I can't remember the name, but they were said to be the spirits of drowned people or murdered people or something like that. The traveler would see what appears to be a woman in the water, and when he'd gut closer, the thing would rise up and attack, it's face and part of it's skin looking decomposed or mumified. It would then attack, attempting to drag the person under. I think one version that I heard of was a corpse like creature that could appear as a beautiful bathing woman from afar, but it is only an illusion, really it is the corpse of a murdered woman, taking her vengance out upon any man who aproaches.
It would be interesting to see spirits of the dead attacking people out of vengance instead of just demons all the time. Like the concept of Hungry Ghosts. Spirits who died traumatically and can not rest, who attack the life force of the living in order to sustain their connection to the mortal realm that they do not yet feel ready to leave. Perhaps the spirit, in it's rage and confusion has gone mad with it's fear of the fade, and is desperately attacking the living to keep hold of the Mortal realm. After all, in the fade, it could be devoured by a more powerful spirit. I'm sure there would be some who are terrified of traveling the fade in their after-life.
This also brings to mind Harpies and Sirens. Creatures of the sea, or of small isolated islands at sea, that survive by luring human prey to a watery death. Or, perhaps, who are abominations, and who lure sailors so that they may possess them before their previously possessed body gets old or ill.
Also, did you know that Nostalgia used to be a name for a mental or emotional disorder? That longing for the past or for something or someone lost, that could be so strong in some people that they become delusional and irrational, and often also depressed. Nostalgia could be an interesting new variety of demon. Perhaps a subset of Desire demon that preys specifically on those who have experienced some great loss or sense of displacement/disconnect from their former life. Maybe like a hybrid of desire demon and sloth, as the depression and lethargy come into play. People with Nostalgia would be lost to dreams and fantasy of what was, and what might have been, so it fits both, yet is different than either.